The present invention relates to a new and improved construction of a gas-blast switch or circuit-interrupter.
Generally speaking, the gas-blast switch or circuit-interrupter of the present development is of the type comprising a set of fixed contacts and a set of movable contacts. Each contact set comprises an arc contact through which there can be axially blown a gas and a rated current contact coaxially surrounding the arc contact. Additionally, there is provided a blast nozzle which is co-movable with the movable contact set. The blast nozzle surrounds the arc contact of the movable contact set, the blast nozzle being closed in the cut-on position of the gas-blast switch by the fixed or stationary arc contact. Furthermore, the blast nozzle flow communicates at its inlet side with a pressure chamber or compartment which can be pressurized during the cut-off stroke, and at the outflow-located end of at least one of the arc contacts there are arranged means in order to axially and outwardly deflect the switching gas which outflows at such end during the cut-off stroke.
Switches or circuit-interrupters of the aforementioned type are known, for instance, from U.S. Pat. No. 4,149,051, granted Apr. 10, 1979, and U.S. Pat. No. 4,144,426, granted Mar. 13, 1979. With these state-of-the-art circuit-interrupters the outflow-located end of both arc contacts is surrounded by a cooler composed of superimposed wound layers formed of metal fabric. This cooler or cooling device cools the effluxing hot switching gas and also at least partially axially deflects its flow. However, such cooling devices or coolers constitute an obstruction for the gas flow or stream which suddenly flows-in during a cut-off stroke. This obstruction can lead to the result that the gas flow effluxing from the blast nozzle, after blowing the switching arc and before this gas flow reaches the outflow-located end of the arc contact, is superimposed to a certain extent upon a "standing wave", i.e. pronounced oscillations are formed in the gas flow departing from the blast nozzle, which alternately result in the formation, and then with an extremely high frequency, of regions having higher and lower pressures in such gas flow. However, a reduced gas pressure also means a reduced gas density, and thus, a reduced dielectric strength of the gas, to the extent that such can still partially be ionized.
A further switch or circuit-interrupter of the previously mentioned type is also known from U.S. Pat. No. 4,095,068, granted June 13, 1978. With this circuit-interrupter the fixed arc contact is retained internally of a contact tube which, at a location flow downstream of the outflow-located end of the fixed arc contact, possesses gill-like circumferential slots bounded by guide vane-shaped ring segments. By means of these ring segments a part of the switching gas departing from the stationary arc contact is deflected outwardly and axially. However, the deflected switching gases, with this construction of circuit-interrupter, arrive at a jacket chamber surrounding the contact tube. This jacket chamber is pierced by cooling metal plates, the surfaces of which are located parallel to the switch axis. Also, these cooling metal plates constitute a hinderance or obstruction for the gas flow which suddenly is formed during the cut-off stroke, which is not only a consequence of the extinguishing or quenching gas flowing out of the pressure chamber, but also a consequence of the sudden heating of the extinguishing gas at the region of the switching arc.
With the heretofore known constructions of circuit-interrupters the heated switching gases must displace a so-to-speak "plug" of initially still cool extinguishing or quenching gas present at the outflow side, and this gas plug only can be displaced against the action of the aforementioned obstruction. This phenomenon can lead to the formation of the previously mentioned oscillation which is superimposed upon the flow (comparable to the oscillations of an air column in an organ pipe), and results in the prior explained undesirable consequences.
A further prior art construction of gas-blast switch or circuit breaker is exemplified by the commonly assigned U.S. Pat. No. 3,941,962, granted Mar. 2, 1976.